36 



is to show tho bearing of what may bo called the nitrogen statistics of 

 the soils, on tho question of the sources of tho nitrogen in the crops, it 

 will be seen that, during tho sixteen years from 180-5 to 1881, both 

 the unraanured plot (;J),aiul tho mineral manured plot (5a), tho yield 

 of nitrogen in tho crops of which declined so sti-ikingly, show a groat 

 reduction in tho stock of nitrogen in the surface soil. The reduction 

 in these later years is considerably greater in tho surface soil of tho 

 mineral manured than in that of tho entirely unmanured plot, tho 

 previous accu.nulation in which had been many more years subject to 

 exhaustion. Taking tho results, however, for the first, second, and 

 third 9 inches, tlie calcnlatcd loss to the depth of 27 inches is approxi- 

 mately the same for tho two plots. The figures recorded for tho first 

 9 inches only are, however, sufficient to show that tho decline in tho 

 yield of nitrogen in the crop, where none has been supplied in manure, 

 is accompanied by a decline in the stock of nitrogen in the soil. 



A further illustration on this point is afforded by tho results for 

 plot lOa. For tho thixteen years, 1852 — 1864, plot 16 received, 

 besides the mixed mineral manure, twice as much ammonium salts as 

 any of the other plots, tho results for which arc given in the table ; 

 and it gave on the average of those years 30| bushels of grain ^er 

 acre per annum. Since 18G4, however, the plot has been left un- 

 raanured, and during the seventeen years, 1865 — 1881, it has yielded an 

 average of only 14f bushels of grain; and in recent years the produce 

 has been very little more than witliout manure, or with purely 

 mineral manure. The table shows that in 1865, that is, after one 

 crop had been removed since the application of the excess of ammo- 

 nium salts, the surface soil still contained considerably more nitrogen 

 than any other plot in the series. In 1881, however, after sixteen 

 years more of cropping without manure, the stock of nitrogen on tho 

 plot was reduced by a greater amount than on any other plot, and to 

 a lower point than on any other of the ammonium plots, excepting 

 plot 10 with the ammonium salts alone. 



Let us now refer to the last three columns in the table, which 

 show, for each of the plots receiving ammonium salts, the amount of 

 nitrogen per acre in the surface soil, more or less than in that of plot 

 5a, with mineral manure alone. All the plots, 7 to 14 inclusive, 

 received the same quantity of nitrogen, namely 86 pounds per 

 acre per annum. But it will be seen that the excess of nitrogen in 

 the surface soils compared with the mineral manured plot 5, varies 

 exceedingly. In fact, it is obvious that the amounts have no direct 

 relation to the amount of nitrogen supplied in the manure. 



The following table (X) will afford some explanation of the diffei'- 



M4^ 



